docs: def get_file_stream(self):
          """
          Return a file stream instance of the upload.
          """
          if self.file_stream:
              self.file_stream.seek(0)
              return self.file_stream
          elif os.path.isfile(self.file_path):
              return open(self.file_path, 'rb')
          else:
              raise ValueError("invalid file {}".format(self.file_path))